This invention relates to power transmission belts and in particular to cogged, or toothed, transmission belts.
2. Description of the Background Art
One conventional form of power transmission belt comprises a cog belt wherein a plurality of teeth project from the body portion of the belt for engagement with suitable pulley teeth in providing a positive drive in the manner of a conventional chain drive.
A serious problem arises in the conventional cog belts of the prior art in that the belts tend to crack at the junction of the tooth with the body of the belt in normal use of the belt. More specifically, the cracks form at the root face of the teeth. Such root face cracking is highly undesirable as it shortens the life of the belt.
One attempted solution to the root face cracking problem has been to provide fabric on the face of the belt defining the teeth.
In one conventional form, the cog belt is formed of a rubber blend. Tensile strength is provided in the belt by means of a plurality of longitudinally extending tensile cords embedded in a portion of the rubber outwardly of the teeth. Conventionally, the cords are provided in a layer of the belt comprising a cushion layer. It is desirable to provide a strong bond between the cords and the cushion layer rubber and to provide a strong bond between the cushion layer rubber and the material forming the teeth of the cog belt.
It is known to form modified rubber blends including in the rubber silane coupling agents, silica, and carbon black. Such blends have been used to provide improved characteristics in rubber structures, such as tires and the like.
Illustrative of prior art patents illustrating such modified rubber blends are British Patent Nos. 1,438,355, 1,439,247, 1,524,077 and 2,038,341, and U.S. Pat. Nos. 3,350,345 and 3,957,718.
Two conventional forms of cog belts are illustrated in U.S. Pat. No. 4,011,766 and 4,034,615.
Another attempted solution to preventing root face cracking in such cog belts has been to use conventional carbon black material, such as ISAF and SAF carbon black materials in the tooth rubber. Such formulated rubbers, however, have not been found to satisfactorily solve the problem because the strength of the rubber is substantially decreased at elevated temperatures, as may occur from high ambient temperatures and from the heat generated during the operation of the belt.
Root face cracking is also found to occur in prior art belts as a result of the impositive bond of the tooth rubber through the load-carrying section rubber to the tensile cords.